1. Field of the Invention
This invention relates in general to a test fixture for simultaneously testing electrical circuitry on both sides of a circuit holder such as a printed circuit (PC) board, wired backplane or rigid or flex ceramics. The invention more specifically discloses a fixture which more accurately places translation pins in contact with the test nodes on both sides of the PC board under test.
2. Description of the Related Art
Circuit testing of a PC board involves making contact with each electrical point on a circuit and sequentially monitoring each and every circuit component and each and every circuit path. In this manner, opens, shorts, missing components, wrong components, backwards or improperly installed components, and out of tolerance components can be individually identified. Hereinafter, the term "PC board" will be used as exemplary of the circuit to be tested and is generally meant to include any other type of circuit that may be tested in the manner described herein.
A complete conventional circuit test system for testing a single-sided PC board includes a controller with measurement circuitry, an electronic switching matrix with bed of nails output, and an interface or fixture imposed between the bed of nails and the test circuit. The controller switches between various multiple contact points on the PC board while monitoring the performance of the component or circuit path. The controller is typically controlled by a test program using a microprocessor or minicomputer.
Each test interface or test fixture must be configured for each specific PC board to be tested. The test interface must make electrical connection between the bed of nails and each test node on the PC board. The typical fixture includes an array of translation pins specifically configured for the PC board, each pin having a first end for electrical contact with a node to be tested on the PC board and having a second end. The second ends of the translation pins form a standardized output grid for electrical connection to the bed of nails input grid of the switching portion. A personality plate includes translation pin bores conforming with placement of the test nodes. The personality plate bores guide the first end of the translation pins to the test nodes. The switching portion includes a standardized input grid of input contacts contacting the output grid. The switching portion includes localized circuitry controlled by the controller to select specific nodes for testing.
Two fixtures, typically an upper fixture and a lower fixture, are used for simultaneous testing of both sides of a PC board. A problem arises with regard to positioning of both fixtures with regard to the PC board. Typically, the lower test fixture personality plate includes tooling pins mounted in tooling pin bores corresponding to tooling bores in the PC board. The PC board is snugly mounted on the lower fixture personality plate tooling pins. The upper personality plate is positioned relative to alignment bores in the lower personality plate. Tolerances are accumulated from location of the PC board tooling bores to the lower personality plate tooling pins to tooling pin bores to alignment bores, through alignment pins to alignment bores in the upper personality plate to the pin bores in the upper personality plate and to the upper tooling pins. The build up of tolerances is such that the upper personality plate is often not correctly positioned relative to the PC board circuitry and its translation pins are not guided to the upper test nodes on the PC board.
Therefore, there has been a need for an improved test interface that provides for more accurate placement of translation pin contacts when testing a double-sided PC board.